1. Field of the Invention
This invention relates to a mirror unit (reflecting-mirror unit), for utilizing X-rays or the like having a short wavelength, in an exposure apparatus, which is used for manufacturing semiconductor integrated circuits or the like, and an exposure apparatus including the mirror unit.
2. Description of the Related Art
Among X-ray exposure apparatuses for exposing a resist, coated on a wafer and provided in the proximity of a pattern on a mask, with X-rays emanating from an illuminating light source, apparatuses which utilize synchrotron orbit radiation (SOR) light as an X-ray light source have been proposed.
The synchrotron radiation light is obtained from an SOR apparatus which emits light on an orbital plane of electrons. While the light from the SOR apparatus has a large beam path in a direction parallel to the orbital plane of the electrons, the light has a very small spread, such that the divergence angle of the light is approximately a few mrad (milliradians), in a direction perpendicular to the orbital plane of the electrons. Accordingly, in order to obtain an exposure region of a few centimeters, which is required for an exposure apparatus, the synchrotron radiation light must be spread in the direction perpendicular to the orbital plane of the electrons. Various methods have been proposed for that purpose. In one method, a plane mirror swings around an axis perpendicular to the direction of the radiation light and parallel to the orbital plane of the electrons. In another method, reflected light is spread in a direction perpendicular to the orbital plane of the electrons by a convex mirror.
A conventional mirror supporting device in a method of obtaining an exposure region using a convex mirror is disclosed in Japanese Patent Laid-open Application (Kokai) No. 5-100096 (1993) filed by the assignee of the present application.
FIG. 13 is a partially-cutaway schematic perspective view of a conventional exposure apparatus. FIG. 14 is an enlarged cross-sectional view of a mirror unit shown in FIG. 13.
As shown in FIGS. 13 and 14, a supporting plate 103, on which a mirror 101 is mounted via a mirror holder 102, is provided within a vacuum chamber 100, so that the entire mirror 101 is provided within the vacuum chamber 100. The supporting plate 103 has a threaded hole 104, and is supported on a mirror supporter 107, which is present outside the vacuum chamber 100, via an internal flange 111, and a supporting rod 106 including an exhaust port 109. The internal flange 111 is connected to the vacuum chamber 100 via a bellows 105, and the mirror supporter 102 is supported on the supporting plate 103 using bolts (not shown). The mirror supporter 107 is positioned by being driven by a driving motor 117, and the tilt of the mirror supporter 107 is adjusted by a tilting plate 116 provided on a reference frame 115. Reference numeral 118 represents a guide for guiding the mirror supporter 107, and reference numerals 119a and 119b represent adjusting screws for finely adjusting the tilt of the mirror supporter 107. A pipe 108 for cooling the mirror is inserted within the supporting rod 106. The pipe 108 for cooling the mirror communicates with a cooling channel 112 formed in the mirror holder 102. Reference numeral 113 represents an O-ring for sealing a connecting portion between the pipe 108 for cooling the mirror and the cooling channel 112.
In order to prevent attenuation of synchrotron radiation light, the mirror 101 is provided in a vacuum. While light having longer wavelengths of light incident upon the mirror 101 is reflected by the mirror 101, light having shorter wavelengths is absorbed by the mirror 101, and the energy of the light is converted into heat. The temperature of the mirror 101 is raised by the heat, and the shape of the reflecting surface of the mirror 101 is deformed by thermal expansion, thereby causing uneven exposure. Accordingly, cooling means, comprising the pipe 108 for cooling the mirror, the cooling channel 112 and the like, is provided for the mirror 101 in order to conduct the heat to the outside. The cooling channel 112 is doubly sealed in order to prevent cooling water from leaking into the vacuum. The mirror 101 is indirectly cooled by cooling the mirror holder 102, which includes the cooling channel 112. Since the interface between the mirror holder 102 and the mirror 101 is in the vacuum, thermal contact resistance is produced.
However, the above-described conventional approach has the following problems. That is, in order to cool the mirror provided within the vacuum chamber, it is necessary to provide the mirror holder, in which the cooling channel for circulating cooling water is provided, and the cooling-water pipe (the pipe for cooling the mirror) within the vacuum chamber. In order to facilitate positioning of the mirror, the mirror is coupled together with the mirror holder, on which the mirror is mounted. Accordingly, every time the mirror is exchanged, the pipe for cooling the mirror must be connected within the vacuum chamber. This causes very inferior operability for exchanging the mirror, and provides for inferior operability overall.
Since leakage of cooling water within the vacuum chamber greatly degrades the degree of vacuum of the vacuum chamber, sufficient countermeasures must be provided in order to prevent leakage of the cooling water. As a result, the configuration of the vacuum chamber becomes complicated, thereby impairing the ease of maintenance and increasing the cost of the apparatus.
In addition, an interface between the mirror and the cooling member (mirror holder) within the vacuum chamber produces thermal contact resistance, thereby reducing the cooling efficiency. Accordingly, there is room for improving the cooling efficiency.